- your store URL;
- page URL with the issue you mention;
- storefront password (if your store has one).
This main one? It seems properly sized. Ideally how'd you like it to look like?
In web design you shouldn't change the image's height via code otherwise it looks squished, therefore the best way is to modify its width to preserve the aspect ratio.
A potential alternative would be making it not full width (in other words: adding the white bars on the left & right whenever the screen is too big, full width on smaller devices and screens):
Although we could make it even smaller I wouldn't personally recommend it since it would stop being aligned with the other sections.